Telephone system



Aug. 19, 1941. vA. WITH ErAL TELEPHONE SYSTEM Filed Feb. 9, 1939 5 Sheets-Sheet 1 Aug. 19, 1941. A. WIRTH Erm.

, TELEPHONE SYSTEM Filed Feb. 9, 1959 5 Sheets-Sheet 2 y. H mg w. N w m WMMUAT VN @www u AP,

' Filed Feb. 9, 1959 5 Sheets-*Sheet 3 ALEX/vage MRT/1X" l ROLAND 55C/rma Arm/ewan?.

Aug. 19; 1941.

A. WIRTH ETAL 1 TELEPHONE SYSTEM Filed Feb. 9, 1939 5 sheetssheet 4 Aug. 19,' ,'194'1.

A. wlR'rH :a1-AL TELEPHONE SYSTEM 5 Sheets-Sheet 5 Filed Feb. 9, 1939 Patented Aug. 19, 1941 TELEPHONE SYSTEM Alexander Wirth and Roland Becker, Frankforton-the-Main, Germany, assignor to Telefonbau und N ormalzeit G. n1. b; H., Frankfort-on-the- Main, Germany, a corporation of Germany Application February 9, 1939, serial No. 255,462 In'Germany February 8, 1938 14 claims. (01.179918) This invention relates to selector-operated telephone systems and in particular to systems comprising a number of exchanges connected by trunk lines. The invention provides new and improved means for controlling the line selectors and, in particular, for sending calling current to a wanted subscriber and also means for sending signal currents to a calling subscriber.

According to one feature of the invention, the nal selector has associated with it switch means for sending out different backward signals in` accordance With the condition of the selected subscribers line. These switch means actuate switch means provided in a repeater connected to the exchange which makes the connection so as to switch in idle and busy signals. On receipt vof the backward signal which characterises that the selected subscribers line is free, the switch means in the repeater cause a control current impulse to be emitted; the switch means in the final selector make the apparatus for the intermittent supply of calling current to a selected free subscriber operative only when this particular control current impulse is received. With this arrangement, the yalternating calling current is therefore not immediately and automatically sent out by the line selector when the wanted subscriber has been found to be free. It is sent out only when a particular control current impulse has been received. lIt is thus possible to control the final selectors in the same way both when the connection is made by a subscriber and when it is made by an exchange operator. rIn connections which are made by an operator, it is usual for the calling current to be sent to the wanted subscriber only after the operator has carried out a particular switching measure. In accordance with the invention, the Wanted subscriber is called only when the calling subscriber has lifted his receiver and the connecting devices are in order. trol current impulse cannot be sent out or transmitted by the repeater which is connected to the calling subscriber. It is also possible, after the nal selector has been set, to transmit further switching operations over the speech line of the connection. For example, current impulses may be sent from the wanted subscribers exchange to the calling subscribers exchange which characterise the former exchange and serve to deterf mine the charge to be made to the calling subscriber for the connection. In this case, the emission or the transmission of the control current impulse may be delayed until these additional switching operations have been transmitted.` The `calling subscriber then receives an appropriate signal upon the reception of the backward signal which indicates that the Wanted subscriber is disengaged. The wanted subscriber is, however, notl yet called. The supplementary switching operations are rst transmitted and then the control current impulse which institutes 4:() When this is not the case, the conthe calling of the wanted subscriber.

In accordance with a further feature of the invention, an exchange is provided with switch means which, on receipt of the backward signalv which indicates that the selected subscriber is engaged,V send out a control current impulse which, in the fnalselector, cause a connection to be made to the busy subscribers line. This considerably `simplifies and accelerates the making of connections through an operator as the operator is automatically connected to a busy line and can inform the subscriber of the existence of an urgent connection.

In accordance with a further feature of the invention, the trunk lines have associated with 4them switch means which, on receipt of certain backward signals, cause the speech lines to be connected. It is thus possible, in a simple manner,`to send the backward signals through the trunklines and through the speech lines which run within an exchange. The speech lines are connected only while talking conditions persist,

i. e. whenv the subscriber replies or when a con- ,this speech line. This makes it possible during talking conditions to connect in each repeater only one relay to each speech line, so that the lspeech currents are very little attenuated.

In accordance with a further feature of the invention. there are provided in the nal selector both circuits for testing whether the selected subscribers line is idle or busy and also a circuit for testing whether a line running to the vsame subscriber is free.` In this group testing circuit is connected a winding of the current impulse relay of the final selector which, when the selected lline is engaged, and also when one of a number of lines belonging tothe same subscriber is free, causes the nal selector to be stepped. This makes it simple to select a free line from a number of lines leading to the same subscriber. Ii an urgent connection is made by an operator when all the lines are engaged, one of the lines which is carrying a not urgent connection is automatically connected to the operator.

These and further features of the invention are explained in the following description of the accompanying drawings, in which:

Figure 1 shows the circuit of a calling subscriber, a nder and a repeater connected thereto;

Figure 2, the circuit of a repeater at the outgoing end of a trunk line;

Figure 3, the circuit of a repeater at the incoming end of a trunk line;

Figure 4, the circuit of a nal selector; and

Figure 5, the circuit of an operators position on a trunk exchange.

Figures 1, 2, 3 and 4 together show the circuits made during a connection between a calling subscriber and a called subscriber; Figures 5, 2, 3 and 4 together show the circuits made during a connection between the trunk exchange and a wanted subscriber. If no trunk line is used, i e. when the wanted subscriber and the calling subscriber belong to the same exchange, the circuits shown in Figures 2 and 3 are not used.

Connections between two subscribers belonging to dierent exchanges When the subscriber ATI (Figure 1) removes his receiver, his calling relay IT (which is a 2- step relay) is energised through the winding I and makes its rst step so. that the contacts ItI, |252 are closed. The contact |t2 closes a circuit through the windings I of the relays IN, IB, |A of an idle finder switch ASI. The relays respond. The contact Inl closes a circuit for the driving magnet DASI of the iinder switch to which is connected an interrupter UPI. The magnet DASI is intermittently energised and steps the wipers of the finder switch. When the wiper c nds the calling subscribers Contact, the follow ing circuit is closed:

-, winding II of relay IT, contact ItI, Wiper c of the finder ASI., relay IC, -I-

The testing relay IC responds and its contact IcI opens the circuit of the magnet DASI while its contact |c2 short circuits its own high ohmic winding. The amplication of the current thus obtained causes the relay IT toI make its second step and open its contacts It3, It/I and |t5. 'Ihe contacts |03 and |04 connect the windings II of the relays IA and IB to the speech wires so that these relays remain energised in spite of the opening of the circuit through their windings I. The contact |c5 closes a circuit for the winding I of the relay IK which responds and by means of its cont-act Ilcl prepares a circuit for another idle finder switch ASE. Also, the contacts |05 and |113 close a circuit for the winding II of the relay IN so that this relay also remains energised. The contact i114 maintains a circuit through the lead ZcZ to the next selector, for example to a group selector. Finally, the contacts |05, I1L3, IgI, m3 and I dI close ra circuit for the relay IE which responds. The contact IeI connects the soiuce of alternating current AZ which emits the exchange signal to the windings I of the relay IA and IB over the contacts |d3 and IbI. The exchange signal is therefore transmitted inductively to the calling subscribers speech wires. When the subscriber has received the exchange signal, he can start the dial.

The iirst impulse emitted when the subscriber dials de-energises the relays IA and IB. The contact Ib2 short circuits the winding II of the relay IB so that this relay cannot respond again. At the same time, the resistance in the feed circuit is reduced. The contact Ibi opens the circuit of the source of alternating current which sends out the exchange signal.

Each time the relay IA drops, an impulse is sent through the wire [a2 by the contact Za3:

{, contacts Ic5, m3, IgI, IaS, Ie2, wire Ia2 In the next selector, which may for example be a group selector, the wire ZaZ has connected to it an impulse receiving relay which sets the selector in accordance with the received impulses.

It is assumed, that when the calling subscriber dials, -a current impulse train is emitted which sets a group selector connected to the wires 10,2, lb2 and .Zc2 in the repeater UTI (Figure 2) from which a trunk line Zad leads to another exchange. When this happens, a circuit is closed through the wire [c3 in which the relay 3B is energised. Consequently, the contact 3c2 energises a relay 3U which, by means of its contacts Sul, energises the winding I of a rel-ay SZ.

The calling subscriber ATI now sends out current impulses which set the selectors of the distant exchange. These impulses are transmitted by means of the contact |a3 of the nder ASI (Figure l) over the trunk line la, |194 to the wire Ia2 which is connected to the wire Za3 in the group selector GW (not shown). The impulses are received in the repeater UTI (Figure 2) by the relay 3A. At each impulse, the relay 3A actuates its contacts 3a| and 3a2 and causes alternating current to be supplied to the trunk line la, Z174. The impulses are thus transmitted through the trunk line as alternating current impulses.

In the repeater UT2 (Figure 3) at the incoming end of the trunk line lad, Zbd, these impulses are received by the relay 4J. The winding I of the relay 4J lies in series with a condenser bridged across the speech wires. The Winding II of the relay IJ is directly bridged across the speech wires The alternating currents arriving through the trunk line la, Ibi. reach it through the condensers lying in the speech wires. This ensures that the relay IJ is energised With reliability with alternating current. At each response, the relay 4J closes by means of its contact M2 a circuit for the relay 4A.

When the first alternating current impulse is received, the seizing circuit through the wire Zc5 of the nal selector LW (Figure 4) is closed by the contact (iii so that the relay 5C responds. Furthermore, the relay 4C of the repeater UT2 (Figure 3) is energised by the contact a2 and locks in a circuit closed at its contact 40|. The contact 403 opens a short circuit for the relay 4E which therefore responds. The winding I of the relay 4Z is also energised by the contact 4cI. Each current impulse is transmitted through the wire la5 by the Contact IIaI so that the winding I of the relay 5A in the inal selector LW is energised. A selector EW of the nal selector LW is set on to the contact connected to the wanted subscribers line by the two impulse trains sent out by the calling subscriber. During the setting of this selector, the relays 5V and 5U are energised. When the last train has been received, the relay 5V releases after a delay and, by means of its contact 5112, closes the testing circuit for the relay 5P.

. lector (not shown).

Desired subscribers line is busy If the' selected line is busy, the relay 5P cannot respond. The relay U drops after a delay as a result of the response of the relay 5E. When, after the relay 5U has dropped, the relay 5V dro-ps, a backward signal circuit through the wires Zb5 is closed by the contact 5u4 in which the winding I of the relay 4K in the repeater UT2 is energised. 'I'he relay 4K responds and its contact Mol closes a circuit for the winding I of `the relay IIS and also locks the Winding II of the relay 4K in a circuit which runs through a slow-acting relay 4L. When the relay 4L responds, its contactIIZl opens the circuit for the 1 relay 4S and short circuits the winding II of the relay 4K. The contact 4lc2 however maintains the Winding I energised in the backward signalling circuit.

The relay 4S (winding I) responds for the duration of the delay in response of the relay 4L and its contacts dsl and 482 connect alternating current to the trunk line lad, Z124. The alternating current impulse sent out is received by the relay 3E in the repeater UTI at the outgoing end of the trunk line; On response of the relay 3E, the relay 3Y is energised by the contact 3e| and its contact 311| prepares a locking circuit which is closed when the relay 3E drops. This locking circuit runs through the Winding I of the relay 3X, which is als-o energised. The short backward impulse energises the relays 3X and 3Y and the contacts 3x2 and 31/2 close the backward signalling circuit through the wire lb3 which is connected to the wire Z112 through the group se- 35 The relay IM which is connected to the line lb2 is thus energised and its contact Im! energises the relay IS. The ccntacts Isl and Im2 short circuit'the winding II of the relay IN. This relay, aftera delay, releases and its contact |113 opens the energising circuit for the relay IE which likewise drops. The contact Im5 removes the short circuit from the winding II of the relay IB. The relay IB responds in the calling subscribers feed circuit and the contacts IbIl m5 and let switch in the source of alternating current BZ which sends out a busy signal to the windings I of the relays IA and IB. The calling subscriber then hears the busy tone.

The seizing circuit running through the wires 102 is interrupted at the contact |114 whether the calling subscriber replaces his receiver or not. The seizing circuit through the wire [c3 is also interrupted in the group selector `(not shown) and the relay 3C in the repeater UTI at the out 55 going end of the trunk'line drops. The circuit of the relay 3U is interrupted at the contact 302. The relay 3A is energised for the duration of the delay in release ofthe relay 3U by the conf tacts 3c4 and 3u3 and its contacts 3a| and 3a2 60 connect the source of alternating current to the trunk line lad, Zbll for 25()I milliseconds. The relays 4J and 4A in the repeater UT2 are consequently energised. The contacts ML24 and 4e2 short circuit the relay 4C which, after a delay, drops. At the end of the alternating current impulse, the relay 4E also drops and the seizing circuit through the wire Zc5 is opened.` When the relay 4C drops, the relays 4Z and 4K are de- 7 prived of current. Y

The opening of the circuit through `the wire causes the relay 5C in -the iinal selector LW to drop. The contact 501 then closes a circuit for stepping the switches EW and ZW into the 7'5 -rest position. The contact 506 and the wiper ZWd close a locking circuit which runs through the wire le5 and energises the winding I of the relay 4K in the repeater UT2. The relays 4K and 4L consequently respond and the relay 4S is energised for the delay in response of the relay 4L so that by means of the contacts 4a| and 4e2, it sends out a short alternating current impulse.

This short alternating current impulse causes the energisation of the relays SY and 3X in the repeater UTI which were deprived of current when the relay 3C dropped. The contact .3g/c closes an energising circuit for the Winding I of 5 the relay 3Z. The contact 322 disconnects the relay 3C from the wire lc3 so that the repeater UTI cannot be seized by the group selector.

It is not until the switch ZW of the inal selector LW has been stepped back into the rest position that the locking circuit through the wire Z051 is interrupted at the wiper ZWd. The relay 4K in the repeater UT2 is deprived of current and` disconnects the relay 4L. The relay IIS is energised for the duration of the delay 25' in response of the relay 4L, and sends back a The repeater UTI is made unseizable in thek same Way when the line selector LW is out of order for one reason or another and must not be actuated.' If, for example, the fuse SSz has blown, the locking circuit through the wire le5 `is maintained closed by the Contact Ssz'.

Desired subscribers Zine is idle If the selected subscribers line is idle, the testing relay 5P responds before the relay 5U has dropped and the contacts 5123 and 5114 connect the speech lines while the contact 5502 prepares a circuit for the relay 5Z which is closed at the contact Sul when the relay 5U drops. At the same time, the backward signalling circuit vis closed through the wire Zb by the contact 5M and is opened again by the contact 522 when the relay EZ responds. This backward signalling circuit causes the relay 4K in the repeater UT2 to respond and the contact 4lc| energises the relay 4L. The winding I of the relay 4S' is energised for the duration in the delay in response of the relay 4L and by actuation of the contacts 48| and 452 sends an alternating current impulse through the line Za4, lbd.. Current iiows vover the wire lb5 for only 50 milliseconds, at the end of which time the relay 4K again drops. A circuit for the relay 4S is closed again by the contacts Mal and M2 for the duration of the delay in release of the relay 4L so that the relay 4S sends back a second alternating current impulse through the trunk line. A circuit is also closed for the relay 4 T by the contacts lIkB and 414 for the duration of the delay in release of the relay 4L. The relay IIT responds and its contact 4tI closes a locking circuit. The contact 4t2 opens the circuit of the winding I of the relay Z and closes a circuit through the windings II of the relay 4Z.

In 'the repeater UTI at the outgoing end of the trunk line the relay 3Y is rst of all energised and then the relay 3X is energised by the relay 3E on receipt of the rst alternating current impulse which is sent through the trunk line to indicate that the selected subscribers line is idle. The contacts 3r2 and 3y2 close the backward signalling circuit through the wire Z173 in which circuit the relay 2J of the metering device ZUG (Figure 2) responds. On receipt of the second alternating current impulse, the relay 3E rst de-energises the relay BY and then the relay 3X. The backward signalling circuit through the wire [b3 is thus again opened. The relay IM in the nder ASI (Figure 2) is energised. The relay IS is energised by the contact Imll. At the end of the backward signal, the relay ID is energised by the contacts Isl and Im2 and its contact Id! opens the circuit of the relay IE and closes a locking circuit. The contact Ie2 now sends an impulse through the wire Ia2 for the duration of the delay in release of the relay IE. The relay ID opens the short circuit of the winding II of the relay IB at the contact Idd so that the relay IB again responds. The source of alternating current VZ which emits the calling signal is connected by the contacts IbI, ICES, and |82 to the windings I of the relays IA and IB for the duration of the delay in release of the relay I S so that this signal is nductively transmitted to the calling subscribers line.

When the relay IS has dropped, the source of current FZ which sends out an intermittent calling signal is connected to the windings I of the relays IA and IB so that that signal is transmitted to the calling subscriber. subscriber is thus informed that the wanted subscribers line is free.

In the repeater UTI, the impulse is received by the relay 3A and is transmitted through the trunk line as an alternating current impulse by the contacts Sal and 3:12. The winding I of the relay 3P and the winding II of the relay 3Z are energised by the contacts 3a3 and 3t3 and the Contact 3p! closes a locking circuit.

In the repeater UT2 at the incoming end of Si;

the trunk line, the alternating current impulse is received by the relay 4J which energises the relay 4A. The contact dal transmits a direct current impulse through the wire 1:15. The

winding I of the relay 4P and the winding III of the relay 4Z are energised by the contacts 40,3 and 4153. The contact 419| closes a` locking circuit.

In the nal selector LW, the current impulse is received by the relay 5A which by means of f the contact 5&2 energises the relay 5V. At the end of the impulse, the relay 5L and the winding I of the relay EQ are energised by the contacts 5113 and 523. The relay 5L closes a locking circuit by means of its contact 51|. The contacts Sql, 5q2 and 5Z2 and 513 close the ringing circuit in which ringing alternating current is sent to the selected subscriber rst from the source TI and then, after the relay 5V has dropped, from the source r2 which acts intermittently.

The connection of the devices of the final selector LW for the automatic calling of the desired subscriber is thus dependent upon the receipt of a current impulse which is emitted automatically by the finder ASI on receipt of the backward signal which characterises that the desired subscribers line is idle. It is thus ensured that the desired subscriber is called only when the calling subscriber has removed his re- The calling ceiver and the connecting apparatus is in order. In other circumstances, the iinder does not send out the impulse and the connecting apparatus cannot transmit it.

On the other hand, it is possible to delay the emission of the calling signal until certain switching operations involving the use of the trunk line have been eiected. If, for example, the charge for the connection depends upon distance, and the zone in which the called exchange lies relatively to the calling exchange is determined by a signal sent back by the called exchange when the connection has been made, a charge determining device (not shown) may be arranged between the nder ASI (Figure 1) and the repeater UTI (Figure 2) which receives the current impulse emitted by the nder ASI but does not immediately repeat it. The relay 4T in the repeater UTZ (Figure 3) was energised by the busy backward signal and its Contact 4t2 had interrupted the circuit through the winding I and had closed a circuit through the winding II of the relay 4A. This circuit runs over the contact gkl of a current impulse transmitter serving a number of repeaters and having two continuously rotated cams. One of these cams actua-tes the contact gkZ so that several trains of impulses are sent out which characterise the exchange in which the repeater is arranged. The contact glcl which is actuated by the other cam is always closed when the cam discs are out of their rest position. If the repeater UTZ is connected to the transmitter by the contact 4t2 when the cams are out of their rest position, a locking circuit is closed through the contact gcI and the winding II of the relay 4Z.

When the cams pass through their rest position, the contact glcl is opened and the relay 4Z drops. 'Ihe contact 422 now closes the current impulse circuit which contains the winding II of the relay 4S and is controlled by the cont-act g7c2. The relay 4S, through its contacts dsl and 432, emits a number of alternating current impulses, for example three trains, which characterise the exchange of the called sub-- scriber.

When the second alternating 'current impulse which indicates that the selected subscriber is disengaged was received in the repeater UTI at the outgoing end of the trunk line, the relay 3T was en'ergised and locked by its contact Btl. By means of itsl contact StZ it opened the circuit through the winding I of the relay SZ. The Contact Sel is therefore now open and the current impulse trains which Icharacterise the called subscriber and which are received by the relay 3E can rnow influence only the relay SY and not the relay 3X. Each of the received irn- Dulses is transmitted by the contacts 30d, 322 and 3y2 to the line Z-b3.

The charge determining device arranged between the lines ZaZ, lb2, [c2 and la, Z113, 103, receives these impulse trains Which are transmitted through the wire Z133, and, in known manner, 4determines therefrom the charge which is to be recorded by the calling subscribers meter when the wanted` subscriber replies. As soon the last of the impulses has been received, the charge determining device sends out the impulse which makes the calling circuit in the iinal se lector LW.

As the impulse which the nder ASI (Figure 1) automatically sends out on receipt of the idle backward signal, is not immediately repeated, it is possible to delay the automatic calling of the selected subscriber. This provides time in which to transmit impulse trains which characterise the called exchange. The transmission `of the signal to the calling subscriber i `specific exchange and, for example, not to other exchanges beyond that exchange, a transmitter which corresponds to the transmitter glcl, gkZ (Figure 3) may also be associated with the re. peater UTI at the outgoing end of the trunk line. Such a transmitter would be switched in in the same Way on energisaton of the relay 3T.

During the automatic calling of the wanted 4subscriber from the nal selectorV (Figure l), the relays IC, IA, IB, IK, IN, and ID are energised in the nnder ASI (Figure 1). In the repeater UTI the relays 3C, 3P, 3T yand 3Z are energised, and in the repeater UT2 the relays 4C, 4E, 4P, 4T and 4Z. When the called subscriber replies, the winding IlI of Ithe relay 5U is energised by the final selectorLW. The contact 5cl unlocks the relay 5L but the winding l1 of the relay 5U remains energised.` The Vcalled subscrib-ers feed circuit now runs through the relay SY and the winding II of the relay 5A. The contact 511| closes the backward signalling circuit through the wire Z195 and the contact 5y3-unlocks the `relay EZ which drops.

Current is thus sent through the backward signalling device Z215 for the duration of the delay in the release of the relay 5Z so as to signal back that the called subscriber has removed his receiver.

If the |connection is to be metered the relay 5A also responds in the feed circuit of the called subscriber. In this case, the relay SZ drops after a delay of 50 milliseconds. If the connection is one for which no charge is to be made, the wire 1h15 of the called subscriber AT'I5 is earthed over a choke coil DR'I5;` When, upon 'the called subscriber having replied, the relay 5L drops, only the relay SY can be energised.

The relay 5A is not energised throughits winding II because, owing vto the parallel connection of the Ichoke coil DR'I5 it does'not receive sunlcient current. f

When, on response of the relay SY, the backward signalling circuit is closed at the contact 511| and the relayZ is unlocked by the contact 5113, this circuit is maintained for about 250 milliseconds because one winding of the relay 5Z is short circuited by the contact 5a4 and the dropping o-f the relay 5Z is therefore greatly delayed.

At the beginning of the transmission of current through the backward-signalling device `Z195, the relay 4Kin `the repeater UT2 is energised and switches in the re1ay4L.' The relay 4S re- Sponds for the duration ofl the delay in response of the relay 4L and sendsan alternating current impulse through the trunk line Zad, Z124. At the end or the backward signal, the relayA 4K first of Aall drops and then `the relay 4L, A`The relay 4S is energised again for the duration of the delay in release of the relay 4L and sends a second alternating current impulse through the trunk line. In `the case of a connection which is to be metered, these two alternating current impulses follow at an interval of milliseconds; in the case of a connection which is not to be metered, they follow at an interval of 250 milliseconds. When the relay 4K in the repeater UT2 responds the relay 4T is unlocked by the contact 4lc3 and drops. When the relays 4K and 4L have dropped, the following circuit is closed for the relay 4G:

The relay 4G responds and its contacts lIgI and 4g2 connect the speech wires. 'Ihe contact 4g3 energises the relay 4D and the contact 494 the relay 4R which is locked by its contact 4rI.

In the repeater UTI at the outgoing end of the trunk line, the rst alternating Icurrent impulse of the backward signal which is received by the relay 3E causes the energisaton of the relays 3Y and 3X. Through the contacts 3x2 and 3112, current is sent through the backward signalling wire Z113. The second alternating current impulse of the backward signal causes first the relay 3Y and then the relay 3X rto drop. The transmission of current through the backward signalling wire Z113 isthus interrupted again. If the connection is one which is to `be metered, current flows over the wire Zb3 for 5G milliseconds; if it is one which is not to be metered, the flow of 'current lasts for 250 mil1i seconds.

On the response of the relay 3Y, the circuit through the relay 3T was opened at the contact 3y4. When the relays 3Y and 3X have dropped, the following circuit is closed for the relay 3G:

+, contacts 302, 312, 311/4, 3x3, 3e2, Sp2, relay 3G,

contact 3t2,

i IG which responds and, .by means of its contact I gI, opens the circuit through the relay ID and locks the relay IG. As in the case of a connection which has to be metered, the energisaton of the relay IM persists only for 50 milliseconds. The relay IM drops before the relay ID opens. The following circuit is now closed through the wiper d of the finder ASI through' which the meter ZM of the calling subscriber is energised.

I-, contacts Ic5, In3, IgI, Id2, Im4, wiper d of the finder ASI, meter ZM,

In the case of a `connection which is not to be metered, the relay IM in the finder ASI is energised for a time sucient to allow the relay ID to drop. When the relay ID drops, the contact Id is opened so that at the end of the backward signal the circuit for the meter ZM of the calling subscriber is not closed at the contact Im4. The connection of the speech line by means of the relay IG is effected in the same manner as in the case of connections which have to be metered.

If a charge determining device is provided which is influenced by the impulse trains which characterise the called exchange, this device receives the backward signal which indicates that the called subscriber has removed his receiver. When this happens, it first of all sends a long impulse through the wire Z123, which, as in the case of a connection which is not to be metered, energises the relay IG without influencing the calling subscribers meter. The charge determining device then sends metering impulses through the wire Z012 which step the meter ZM in accordance with the charge to be made. AIf the charge depends also upon the duration of the connection, metering current impulses may be sent out periodically by the device during the connection, for example, at the end of the third and each subsequent minute etc.

When the calling subscriber replaces his receiver, the relays IA and IB in the finder ASI (Figure 1) are de-energised. The contact Ia2 short circuits the relay IN which drops. The contact In opens the circuit through the relay IC. All the relays are thereby de-energised. When the contact Ine opens, the circuit through the wire Zc2 is also opened so that the group selector is released. The circuit through the wire Zc3 is thus opened.

In the repeater UTI, the relay 3C drops, so

that all the relays return to their rest position.

The relay A is energised by the contacts '3:24 and 3a3 for the duration of the delay in release of the relay ZU and by means of its contacts 3al and 3:12, sends a long alternating current impulse through the trunk line.

In the repeater UT2, the relay 4C is short circuited by the relays 4J and 4A which receive the long alternating current impulse. The relay 4C Vdrops and opens the circuit through the other relays. On receipt or a long alternating current impulse, the relays AJ, 4A and 4E also drop. The circuit through the wire Zc5 is opened so that in the iinal selector LW the relay 5C drops and, in known manner, causes the final selector to be released.

If the connection has been made to a subscriber such as the subscriber AT'II who has a number of lines, the iinal selector LW automatically selects a free line from among them. When the Wipers EW of the selector are set on the first line ZaII, Zb'II of thi-s -subscribers line, the relay 5V which was energised during the setting is deenergised. The contact 5122 closes the testing circuit for the relay 5P through the contact 5u3 which is still closed. The relay 5P only responds if the line is idle The contact 5124 closes an energising circuit for the winding I of the relay E which responds and closes its contact 5e5. If, at this moment, the testing relay 5P has not responded because the rst line Za'II, ZbII is busy, the following circuit is closed through the winding III of the relay 5A:

+, contacts 5c4, 5x2, 511|, 5]"4, Set, winding III of relay 5A, Contact 5u5, wiper EWd, line Zd'II, contacts t'IZ and t'l3 or t'M,

The relay 5A is energised in this circuit. The contact 5cl closes a circuit for the stepping magnet DEW and the contact 5:12 again energises the relay 5V. The wipers of the final selector are stepped on to the next contact.

Let it be assumed that subscriber AT'II has four lines laII, Zb'll, to Za'M, 1h14. In the contact bank wiped by the wiper EWCZ, the contacts which correspond to the iirst three of these lines are connected together and are connected to the battery by the contacts t'I I-t'M connected in parallel of the separating relays Til-T14 of the four lines. With this arrangement, as long as one of the lines Z'I I-Z'M is idle, one of the relays TTI-T214 is not energised and the wiper EWd is connected to the battery so that the relay 5A is energised and causes the wipers to Abe stepped. The contact associated with the last line 114 and wiped by the wiper EWd is connected to earth so that the wiper cannot be stepped beyond it.

If, when the selector is set on the first line lI, all the lines are busy, the relay 5A is not energised and when the relay 5U has dropped, the backward signal indicating that the subscriber is busy is given through the contact 5a4.

If there is an idle line, the wipers are stepped until the testing relay 5P responds, whereupon, in the described manner, the backward signal indicating that the called subscriber is free is given.

Connection between a distant exchange and a subscriber belonging to another echange The relay AR in the distant exchange FP (Figure 5) is energised by a call over the long distance line la, Zb which switches in the locking relay 6H. The contact 6h2 switches in the lamp AL and the operator asks for the required number by setting over the switch AT.

To make the connection to the wanted subscriber, the operator actuates the switch VT so that the winding I of the relay 6N is energised by the contact VT4. The winding II of the relay 6N is locked bythe contacts EnI and 6n3 in which a relay 5B is also energised. The relays 6C and 6E are also energised. 'I'he contact Bbl closes the seizing circuit through the wire Zc3. This circuit may lead to a group selector which selects the repeater UTI at the outgoing end of a trunk line so that the relay 3C is energised. The further impulse trains which the operator sends out by means of the numerical switch nsI and the relays 6J and 6A are received by the relay 3A which transmits the impulses through the trunk line Zall, Zb4 by means of the contacts 3aI and 3a2.

In the repeater UT2 at the incoming end of the trunk line, the current impulses are received by the relay 4J and are repeated by the relay 4A. The relays 4C, 4E and 4Z are energised on receipt of the first impulse. The final selector LW is set in known manner by the impulses received from the relay 5A. During receipt of the last impulse train, the relays 5U and 5V in the final selector are energised. When, on receipt of the last impulse the slow-to-release relay 5V releases, a circuit for the relay 5E is closed at the contact 5114. The relay 5E responds and opens the circuit through the relay 5U at the contact 5e2. The testing circuit for the relay 5P is maintained for .the duration of the delay in the release of the relay 5U.

If the wanted subscriber is free, the relay 5P responds and the contact 5p2 prepares a circuit for the relay 5Z. When the relay 5U drops, the backward signalling circuit through the line Zb5 is closed by the contact 5nd. At vthe same time, the contact 5uI closes a circuit for the relay 5Z which responds after a delay and by actuating its contact 522 opens the backward signalling circuit. In the repeater UT2, the relay` 4K is energised over the line `1125 by the backward signalling impulse which lasts 50 milliseconds, and switches in the relays 4S and 4L. The relay 4S is energised for the duration of the delay in response of the relay 4L and, by means of its contacts 4s| and 4s2, sends back a short alternating current impulse through the trunk line Za4, lb4. At the end of the backward signalling impulse received through the line Zb'5, the relay 4K drops and, for the duration of the delay in release of the relay 4L, again closes the circuit for the relay 4S which sends` out a second backward signalling impulse through the trunk line. The contacts 41c3 and 414 cause the relay 4T to be energised. The relay 4T is then locked by the contact 4t| and the contact 4t2 opens the circuit through the relay 4Z. A circuit is thus prepared for the transmitter which sends out the impulse trains which characterise the called subs'cribers exchange. The relay 4Z is, however, very slow in releasing because of a condenser which is connected in parallel with its winding I. i v

In the repeater UTI, the rst backward signalling impulse received from the relay 3E causes the energisation of the relays 3X and 3Y. The backward signalling circuit through the li-ne Zb3 is closed by the contacts 3x2 and 3y2; the second backward signalling impulse which occurs after 50 milliseconds causes de-energisation of the relays 3Y and3X which drop one after the other. The contact 3112 opens the backward signalling circuit through .the line Zb3. The relay T is energised by the contacts 3y4 and 3x3 and is locked by its contact`3t| while its contact 3152 de-energises the relay 3Z. The condenser which is connected in parallel with the winding I of the relay 3Z is disconnected on energisation of the relay 3C so that the relay 3Z drops without delay.

. At the distant exchange FP, the 50 millisecond backward signalling impulse is received by the relay 6M which, by means of its contact 6m|, energises their relay BS. The relay 6N which is now energised, asiare the relays 6C, 6E and 6B, because of its delayed release does not drop in spite of the opening of the locking circuit through its winding II.

When, at the end of the backward signalling impulse, the relay 6M drops, the relay 6D is energised through its winding I by the contact Bml, the short circuit of the winding I being opened at the contact 65|. The contact 6d| closes a locking -circuit through the winding II of the relay 6D. The contact 6d3 closes a circuit for the relay 6A which, by means of its Contact 6al, sends out an impulse through the line la3. The relayv 6F is energised by the contacts 6a.3 and 653 and its contact 6j2 opens the circuit through the relay 6A. After the delayed release of the relay GS, the circuit through the relay 6F is opened at the -contact 6s3. For the duration of the delay in the dropping of the relay 6F, a circuit is maintained by the contacts 6s2 and 632 through the relay 6A which sends out `a second impulse through the line la3'. Also, the

winding I of the relay 6K is energised by the contacts 653 and 613 and is locked b'y its contact 67cl. On receipt of the 50 millisecond backward signal which indicates that the wanted subscriber is disengaged, two impulses are sent out from` The two impulses sent out from the exchange,

CTI

FP are received in the repeater UTI by the relay 3A which transmits them over the trunk line by means of its contacts 3M and 30.2. On receipt of the iirst impulse, the contacts 3a3 and 3t3 close a circuit for the winding I of the relay 3P and the Winding II of the relay 3Z.r

The relay 3P is locked by its contact 323|. The relays 3C, 3U, 3T, 3P and 3Z are now energised.

In the repeater UTZ, the two alternating current impulses are now received by the relay 4J which causes the relay A to repeat the impulses over the line Za. On receipt of the first impulse, the contacts 4a3 and 4t3 close a circuit for the winding I of the relay 4P and for the winding III of the relay 4Z. The contact 410-1 closes a locking circuit. The dropping ofthe relay liZis prevented by the energisation of the winding III of the relay 4A, so that the common transmitter cannot send out the current impulse trains which characterise the exchange of the wanted Isubscriber by means of the contact ylc2. As the connection is made by the operator who estimates the charge, `the emission of these impulses is not necessary. They are only necessary when a connectionto another exchange is made by an ordinary subscriber. In this case, a charge determining device may be arranged in the path of the connection which prevents the transmission" of one or two control impulses following upon the backward signal which characterises that the wanted subscriber is disengaged, so that the relay 4A drops in the repeater UT2. Ii, however, one or two control impulses immediately follow the transmission of that signal, the relay 4Z is again energised so that the relay A cannot drop.

In the nal selector LW, the two control impulses sent out by the exchange FP are received by the relay 5A which energises the relay 5V. On `receipt of the rst impulse, the contacts 5173, 5a3, 523 and 54 close a circuit through the relay 5L and the winding I of the relay SQ. Both relays respond and are locked by their contacts 51| and 5q4. The contacts Sql, 5q2, 512 and 513 close the calling circuit in which calling alternating current is sent to the wanted subscriber in the first place from the source rl and, when the relay 5V has dropped, from the'intermittently operating source r2. On receipt of the second impulse, the winding I of the relay 5F is energised by the contacts 5113, 5&3 and 514 and is locked by its contact 5f|. The contact 513 short circuits the windings I and II of relay SP so that the selected subscribers line cannot be seized by another high grade connection.

When the called subscriber removes his receiver, the relay 5U is energised through its winding III. The `contact Bul opens the locking circuit for the relay 5L. The contacts 512 and 513 switch in the source of alternating current and the feeding relays 5Y and 5A. The relay EY in the feed circuit is energised and its contact Syl ,closes the backward signalling circuit through the line Z195. The contact 5113 opens the locking circuit for the relay 5Z which, after dropping,`in the backward signalling circuit is again interrupted by the contact '522. The contact 5y4 -ha's connected the speech line.

In the -repeater UT2, the relay 4K is energised at the beginning of the 50 millisecond backward signalling impulse which denotes that the called subscriber has removed his receiver. The contact 470| energises the relay 4A and the relay 4S is energised for the duration of the delay in the response-of the relay 4A and sendsV out a short alternating current impulse through the trunk line m4, Z134. On response of the relay GK, the contact 4703 opens the locking circuit for the relay T which drops. At the end of the back- Ward signalling impulse which is received through the line Z215, the relay K is deprived of current and the relay 6L, after a delay, drops. The relay SS is again energised for the duration of the delay in release of the relay 4L and sends out a second short alternating current impulse. When the relays K and 4L drop, a circuit is closed for the relay 4G. 'The contacts S9-fl, 49| and 492 connect the speech lines so that all the branches are cut off from the speech lines. The contact 494 closes a circuit for the relay 4R which is locked by its contact lirl.

In the repeater UT|, on receipt by the relay E of the first alternating current impulse of the backward signal which indicates that the called subscriber has removed his receiver, the relay 3Y is rst energised and then the relay 3X. The backward signalling circuit through the line lbs is closed by the contacts 3x2 and 392. The contact 394 unlocks the relay 3T which drops. The second alternating current impulse, received at an interval of 50 milliseconds, causes first the relay 3Y and then the relay 3X to be deenergised by the relay 3E. The contact 392 opens the backward signalling circuit. When the relays 3Y and 3X drop, a circuit is closed for the relay 3G. The contact 39| energises the relay 3R which is locked. The contacts 392 and 393 connect the speech lines and sever all branches from the speech lines.

In the exchange FP, the 50 millisecond back ward signalling impulse transmitted over the line Zb3 is received by the relay EM. The contact SM2 energises the relay SZ. When the relay QM drops, the relay 6G is energised and its contact 69| connects the speech lines while its contact 692 disconnects the lamp L2. When the called subscriber replaces his receiver, the relays Y and 5A in the nal selector LW are de-energised. The contact 59| earths the line Z125 and the contact 595 connects the line Za to the battery. By means of this ow of direct current, the winding II of the relay 4J in the repeater UTZ which is at other times energised by alternating current impulses received through the trunk line, is energised. rThe relay 4J is bridged across the lines Za and lb5 and, therefore, the winding II responds to a direct current, By means of its contact M2, it energises the relay 4A, the contact la of which opens the circuit for the relay 4G. The winding I of the relay 4K is thus again connected to the line [b5 and is energised by the direct current flowing through this line. The contact 476| energises the relay 4L so that the relay 5S is also energised for the duration of the delay in the response of the relay BL and sends a short alternating current impulse through the trunk line.

In the repeater UTI, this alternating current impulse which denotes that the called subscriber has replaced his receiver is received by the relay 3E which, at its contact 362 opens the circuit for the` relay The contact Sel energises the relay BY and then the relay 3X. The line ID3 is earthed by the contact 3x2, 392 and 393 while the line 19,3 is connected to the battery by the contact 92.

The relay 5M in the exchange FP which is bridged across the lines is energised by the direct current and its contact 6m2 opens the circuit through the relay 6G. The contact 6g| again applies potential to the relay 6M so that it is kept energised by the flow of current through the line ID3'. The contact 692 closes the circuit of the lamp L2 which lights up. The operator is thus informed that the subscriber has replaced his receiver.

By depressing and releasing his receiver hook, the subscriber will cause the lamp L2 to flicker. Each time the hook is released, the relay SY in the nal selector LW is energised and its contacts 59| and 594 disconnect the battery from the line Za, Z135. In the repeater UT2, the relays 4K and L drop one after the other. The relay 4S is momentarily energised and sends an alternating current impulse through the trunk line. The relay 4G is again energised and connects the speech lines. In the repeater UTI, the alternating current impulse is received by the relay 3E which de-energises the relays SY and 3X. When these relays drop, the relay G is energised and connects the speech lines. At the exchange FP, the relay EM is defenergised and its contact 6m2 closes a circuit for the relay 6G, the contact Bgl of which connects the speech line While the contact 692 disconnects the lamp, The lamp L2 thus ilickers in phase with the movements of the receiver hook.

If the operator wishes to call back the called subscriber after he has replaced his receiver, she momentarily actuates the calling key RT so that the contacts VT3 and VTE are closed and the relay 6A energised. The contact Sal then sends an impulse through the line la. In the repeater UTI, the impulse is received by the relay 3A and is repeated over the trunk line as an alternating current impulse by the contacts 3a! and 3a2. In the repeater UTZ, the alternating current impulse is received by the relay 4J and is repeated over the line la by the relay QA. In the final selector LW, the relay 5a responds and energises the relay 5V. The contacts 5123, 5113, 523, 5f2 and 5x4 close a circuit for the relay 5L for the duration of the delay in response of the relay 5V and the contact 512 connects the source of calling alternating current tothe speech line. When the subscriber replies, the same operations take place as have been described above.

The wanted subscribers line is busy If the wanted subscriber is engaged, the relay 5P in the line selector LW does not respond before the relay 5U. The Contact 5u4 closes the backward signalling circuit through the line LDS. In the repeater Ut, the relay 4K is energised and switches in the relay 4L. The relay 4S is energised for the duration of the delay in response of the relay 4L and sends out a short alternating current impulse through the trunk line.

In the repeater UTI at the outgoing end of the trunk line, this alternating current impulse causes the relay 3E and then the relays 3Y and 3X to be energised. The backward signalling circuit through the line Z123 is closed by the contacts 3x2 and 392.

At the exchange FP, the relay 6M is held energised by means of this continuous backward signal which indicates that the wanted subscriber is engaged. The contact tml unlocks the relay 6N which drops after a delay and at the same time closes a circuit for relay SS. When the relay 6N drops, the relay 5A is energised by the contacts 6s2, 6115, 6023, E193 and 6/2 and its contact Bal sends out an impulse through the line Za3. The contacts 6a3 and 6s3 energise the relay 6F and thecontact Bf2 :le-energises the relay 6A. The,

relay BF is locked by its Contact Iifl.

In the repeaterUTl, the impulse is received by the relay 3A and is repeated as an alternating current impulse by the contacts 3a| and 3a2. The contacts 3a3, 3t3, 3114 and`3y5 close a circuit for the relay 3F and the winding II of the relay SZ. The relay 3F is locked by its contact 3H.

In the repeater UTE,` the alternating current impulse is received by the relay 4J which energises the relay 4A. The contact 4aI sends an irnpulse through the line Za5. The contacts 4a3, 4t3, 4113 and 4164 close a circuit for the Winding I of the relay 4F and the winding III of the relay 4Z. The relay 4F is locked by its contact 4JI,

In the line selector LW, the relay 5A is energised momentarily and energises the relay 5V.

A A circuit 4for the winding II ofthe relay 5U and for the winding I of the relay 5X is closed by the contacts 5113, 5:13, 523 and 52 for the duration of the delay in release of the relay 5V. The concontact 5ml closes a locking circuit for the relay 5X. Thel contact 511,4 opens the backward signalling circuit through the line Z115.

In the repeater UT2, the relays 4K and 4L dropone after the other. The relay 4S is ener'gised for the duration of the delay in release of the relay 4L and sends an alternating current impulse through the trunk line. The contact 412 now energises the winding II of the relay 4P. In the repeater UTI, the relay 3E is energised by thev alternating current impulse and de-energises the relays 3Y and 3X. The contact 3y2 opens the backward signalling circuit through the line lb3, and the winding II of the relay 3P is now energised by the contact 3f2. Inthe exchange FP, the relay BM drops and opens the circuit through the relay BS. The contacts Emi and 6m3 energise the winding I of the relay 6D and the winding II of the relay 6K. The contact GdI locks the winding II of the relay 6D and the .contact SICI locks the winding I of the relay 6K. The lamp L2 is caused -to iiicker by the interrupter UPEI.

The response of the relay X of thelnal selector LW causes the winding I of the relay 5P to be short-circuited when the relay 5V drops. If the selected subscribers line is engaged bya less importantA connection, the relay 5P responds through its windings II and III and the contact 5172 opens the circuit through the relay 5U. The relay 5U drops and then its contact 5u4 closes the backward signalling circuit through the line Ibi and its contact Sul closes a circuit for the relay 'SZ which, after a delay, responds and opens the backward signalling circuit again at the contact 5.22. I I

In the repeater UTZ, the relay 4K is energised at the beginning of the short, 50 millisecond backward signalling impulse and energises the relay 4L. The relay 4S is momentarily energised and sends the alternating current I impulse through the trunk line.

At the'end of the backward signalling impulse received through the line Z115, the relays 4K and 4L drop one after the other. The re1ey 4s is momentarily energised a second time and emits a second alternating current impulse. The relay 4G is now energised by the contact 4p2. The contacts 4gl and 4g2 connect the speech lines. The contact 4g4 energises the relay 4RI which islocked by the contact 4rl.

inthe repeater UTI, the relays 3Y and 3X are energised by the first alternating current impulse by means of the relay 3E. The @Olitacts 3x2 and 3y2 close the backward signalling circuit through the line 1223. The relays 3Y and 3X are again de-energised by the relay E on receipt of the second backward signalling impulse which arrives after 50 milliseconds. The relay 3J is now energisedv by the contact 3102. The contact 3gI energises the relay 3R which is locked by its contact 31I. `The contacts 3g2 and 3h3 connect the speech lines so that the backward signalling circuit is opened. `In the exchange FP, the relay BM is energised by the 50 millisecond backward signalling impulse. The contact 6m2 closes a circuit for the relay GZ. When the relay 6M drops, the relay 6G is energised and its contact Ggl connects a speech line. The contact 692 closes a circuit for the lamp L2 which burns dimly. This denotes tothe operator that she is connected to the wanted subscriber. The speech lines are connected in the repeaters yand all the branchesare cut oir from the,Y speech lines. In thevnal selector LW, the connection is effected by the contact 51:4, a condenser and the contacts Sql, 5113 and 5114. The operator can thus speak to the subscriber who is engaged on an ordinary call and tell him that there is a long distance call for him.

HadV the subscriber been engaged on a long distance call, the windings II and III of the relay 5P could not have been energised. Consequently, the backward signal which has just been described and which causes the speech lines to be connected in the repeaters is suppressed. At the exchange FP, the lamp L2 liickers and indicates to the operator that the wanted subscriber is busyvon a long distance call. When the operator has informed the subscriber to whomshe was connected of the existence of a long distance connection, she puts back the exchange key VT into the rest position and thereby brings the connection into a state of waiting. The-relay 6A is energised over the contacts 602,511.2, and VTS. The contacts 60|, Gal and Bel earth the line la3' and potential is applied to the line Z193 by the winding I of the relay BT and the contacts 6e2, 6a2, 624 and 6114. In the. repeater UTI, the winding II of the. relay 3E is bridged across the speech lines le3, Z193` The direct current iiowing through the speech wires energises the relay 6T at the exchange FP and the vrelay 3E in the repeater responds. Thecontact 6t2 closes a circuit through the winding I of the relay 6N which is locked by its contact6n3. l In addition,Y

the contact Btl closes a locking circuit through the winding II of the relaylBT. In the-repeater UTI in which the relay 3E (which is otherwise only energised by alternating current impulses received through the trunk line Za4, Z194) has been energised by alternating currents, the circuit through the relay 3G is opened at the contact 362. The contact 392 again connects therelay 3E to the line la3. As the delay in response of the relay 6N in the exchange FP is-shortened so that the relay responds at the moment when the relay 6A in the repeater UTI is still energised, the relay 3A is momentarily energised by the current fflowing through the line la3 and sends an alternating current impulse through the trunk line. f

In the repeater UTZ, this alternating current impulse is received by the relay 4J which energises the relay 4A. The contact 4a4 de-energises the relay 4G which disconnects the speech tarily energised and consequently energises the relay 5V. The contact S122 opens' the circuit through the relay 5P and the relay SP drops. The contact Sp2' opens the circuit through the relay SZ and closes a circuit for the relay 5U. For the duration of the delay in release of the relay SV and of the relay SZ, a circuit is made through the contacts 5113, 5a3, 523 and S1114 for the windingy II of the relay 5X and the winding I of the relay SF. The relay SF responds and its contact SfI closes a locking circuit through the winding II. The energising circuit for the winding I of the relay 5X is thereby opened so that this relay' drops. In the nal selector, the relays 5C, SE, 5U and SF are now energised.

In the repeater UT2, the relays 4C, 4E, 4Z and 4R are energised. The relay 4F is de-energised owing to the dropping of the relay 4G. In the repeater UTI, theA relays 3C, 3U, SZ and 3R are energised. The relays 3P and 3F have been de-energised by the dropping of the relay 3G.

When the wanted subscriber terminates the call on which he is engaged (the connection for the long distance call having been prepared), the relay' 5P of the nal selector LW can respond through its windings I, II and III. The idle signal, the control impulses which switch in the automatic calling apparatus and the backward signal which indicates that the called subscriber has removed his receiver are then transmitted in' turn in the same way as they were when a connection was m-ade to a free subscriber.

If the operator wishes to sever the existing' connection to the wanted subscriber, she sets the exchange switch VT and actuates her starting key TT for a short while. The relay TR in the exchange FP is thus energised and closes a circuit for the driving magnet DT of a switch. The wiper wtI of this switch causes the relay 6J to be actuated so that it rst emits a number of current impulses and then, after a pause one further current impulse. These current impulses are transmitted through the line Za3 by the contact Bal of the relay 6A.

In the repeater UTI, the current impulses are received by therelay 3A and are repeated as alternating current impulses. In the repeater UT2, the alternating current impulses are received by the relay 4J and are'repeated by the relay 4A. In

the line selector LW, the relays 5A and 5V are energised by the impulses of the rst train. On receipt of this train, the contacts Sc4, 5x2, Sp2, 5,74 and 5115 earth the testing wire of the subscribers line so that the testing relay of the nal selector which holds this subscriber engaged is short-circuited and caused to drop. In the pause following the receipt of the impulse train, the relay 5V drops so that the relay SP can respond and, by means of its contact Sp2, interrupt the circuit of the relay 5U. By the further current impulse which is then received, the relays 5A and SV are energised. For the duration of the delay in release of the relay SV, a circuit is now closed through the relay SL and the winding I of the relay SQ by the contacts 5123, Sa3, 523, Sf2 and 5x4. Both relays respond and their contacts Sql, 5q2 and 512, SZ3 cause the calling circuit to be sent to the wanted subscriber. As the subscriber has not yet removed his receiver, the relay 5U (winding III) at once responds and unlocks the relay SL. 'I'he relay SQ is kept energized by its winding II. When the relay 5L drops, the relay SY and the winding II of the relay SA are energized in the feed circuit of the wanted subscriber. On response o'f the relay 5P (as a result of the dropping of the relay 5U), the contact Su4 closes the backward signalling circuit through the line ZbS for the duration of the delay in response of the relay 5X. On response of the relay SY, the contact Sy3 unlocks the relay SZ and the contact SyI closes the backward signalling circuit a sec-- ond time for the duration of the delay in the response of the relay SZ. All the speech lines are then connected and all the branches are cut off from them.

In the repeater UT2, a relay 4K is energized at the beginning of the rst backward signalling impulse and energises the relay 4L. The relay 4S is momentarily energised and sends out the alternating current impulse. At the end of the irst backward signalling impulse received through the line ZbS, the relays 4K and 4L drop one after the other. The relay 4S is momentarily energised and sends vout a second alternating current impulse. The contacts 4cI, 4fI, 47c3, 4Z4 and 4p4 energise the relay T which is locked by its contact 4H. The alternating current impulse now received through the trunk line and sent out from the exchange FP after the impulse train which severs the existing connection energises the relay 4A. The contacts 4a3 and 4t3 then energise the relay 4P which is locked by its contact 4pI At the beginning of the backward signalling impulse which is sent through the backward signalling line |115 on response of the relay SY in the final selector, the relays 4K and 4L again respond one after the other so that the relay 4S sends out an alternating current impulse. The contact No3 unlocks the relay 4T which drops. At the end of this impulse, the relays 4K and 4L drop one after the other. 'Ihe relay 4S is momentarily energised and sends out an alternating currentv impulse. When the relay 4L drops, the relay 4G is energised by a contact 4Z4 and connects the speech lines.

In the repeater UTI, the relays 3Y and 3X are first energised and then again de-energised by the two alternating current impulses which are received through the trunk line 50 milli-seconds after the existing connection has been severed. TheV backward signalling circuit through the line Zb3 is closed for 50 milliseconds. On de-energisation of the relays 3Y and 3X, a momentary circuit is made by the contacts 3114 and 33 for the relay 3T which responds and is locked by its contact 3tI.

The control impulse which is sent out by the exchange FP after the train which severs the existing connection, energises the relay 3A so that the contacts 3a3 and 3153 energise the Winding I of the relay 3P. The relay 3P responds and is locked by its contact Spl. The next two alternating current impulses which denote that the wanted subscriber has removed his receiver energise the relays 3Y and 3X. These relays are then de-energised. The backward signalling circuit through the line Zb3 is thus closed a second time for 50 milliseconds. On being energised, the relay SY unlocks the relay 3T. When the relays 3Y and 3X de-energise, the circuit through the relay 3B is then closed so that this relay responds and connects the speech line.

In the exchange FP, the relay 6M, the contact EmI of which energises the relay ES, is energised by the first 50 millisecond backward impulse received after the existing connection through the line Z193 has been severed. The Contact 634 unlocks the relay 6T which drops. At the end of the impulse, the relay 6D (winding I) is energised by the contact Gml, the short circuit of the winding the speech lines and its contact 692 switches oi the lamp. Ordinary talking conditions now exist- When the subscriber replaces his receiver, the lamp L2 is again switched on in the manner described. i

Connection Vto a busy subscriber having c number of lines If the exchange FP is to make a connection to a subscriber having a number of lines, for example, the lines lll-114 which lead to the subscriber ATII the switch EW ofthe final selector LW is set on tothe first` of these lines by the impulsessent out by the exchange. If, on receipt of the last impulse, the `relay 5v drops, the contact 5124 energises the winding I of the relay 5E so that the contact5e2 opens the circuit through the relay 5U. A testing circuit is made for the relay 5P for the duration of the delay in the release" ofV the relay 5U. If the relay.5P cannot respond because the rst of the lines is busy, a circuit is closed through the wiper EWd. The contacts associated with the various lines of the subscriber ATTI in the contact bank wiped by the wiper EWd are connected together except for the contact` associated with the last of the line. The contacts which are;connected together are connected to the battery by parallel connection of the contacts t1l-t14 of the separating relays of ,f

all the lines as long as one of the lines is idle.

The relay 5A is energised in the following circuit: A

+, contacts 504, fsa-2, spl, 511,566, winding n1 of the relay 5A, contact 5MG, wiper Ewd, contacts t'M, f

The contact 5cl then energises the driving magnet DWE and causes the wipers of the switch EW to be moved forward by one step.

At the same time, the contact 5a2 energises the relay 5Vso that the contact 5124 opens the circuit through the relay` 5E which. drops. When the relay 5V drops, the testing of the second line is effected. The Vwipers of the switch EW are stepped until an idle line is found. The relay 5U is still energised by the contacts 5e2 and 5cl so that it does not allow its armature to drop. When an idle line is found, the further switching operations are effected inthe manner already described. u

If however, all the lines are busy, the circuit for the winding III of the relay 5A cannot be made when the first lineis vtested because all the relaysT'lI-T'M are energised. When the relay 5U drops, the backward signalling circuit through the line lb5 is closed at the contact 5u4. 'I'he backward signal which denotes that the wanted subscriber is busy causes the relay 6N in the exchange FP to d rop in the manner described and an impulse to be emitted-which is transmitted through the trunk line. In the line selector LW, this impulse is received by the relay 5A, which energises the relay 5V. A circuit for the winding II of the relay 5U and for the winding I of the relay 5X is closed for the duration of the:delay in release of the relay 5V. Both the relays respond 'and the contact 5ml closes a locking circuit. The contact 5x2 short circuits the winding I ofthe relay 5P, so that only the windings II and III of the relay 5P are in the testing circuit. If the first line of the subscriber ATTI is kept engaged by a connection of less importance, the relay 5P cannot respond and the further operations take place in the manner already described. If, however, the first line is engaged by a long-distance call, the relay 5Pcannot respond through its windings II and III. The winding III of the relay 5A lies in the following circuit: contacts 504, 5e2, 5x2, 514, 566, winding III of relay 5A, contact 5x5, The relay 5A is energised in this circuit and causes the wipers of the Vswitch gear EW to be stepped and the relay 5V to be energised.` The contact 5112 opens the circuit through lthe relay' 5A. When the relay 5V drops, the second line of the subscriber ATTI is tested. If this line is also engaged by an important (long distance) call nthe selector is again stepped. If all the lines are engaged on important calls, the relay 5P cannot be energised through its windings II and III on anyof the lines. When the wiper of the switch gear EW has been stepped on to the contact of the last line, no further stepping takes place. The contact associated with this line and which is wiped by the wipers EWd is permanently earthed. The exchange official receives no backward signal, and is thus informed that all the lines are engaged on important calls. If, however, the wipers of the switch EW reach a line which is engaged on an unimportant call, the relay 5P responds, connects the speech lines and causes a backward signal to be given in the manner described, so that the exchange operator is connected to this line. The further operations take rplace in the manner already described.

Instead of being emitted automatically from theexchange FP, the various control current impulses may be sentout by the operator." In particular, it may be advisable for the receipt of the Vbackward signal which denotes that the wanted subscriber is engaged simply to cause the appropriate lamp to be switched in, so that the control impulse which, in the line selector, causes the connection to be made to the busy line, must be sent out by the operator of the exchangeFP.

1. In an automatic telephone system, a plurality of subscribers lines, a connector with means for transmitting" a backward signal according Vas the wanted subscribers line is idle and with means for emitting ringing current to an idle subscribers line, means connected to a calling subscribers line for receiving said backward signal and therebylfor transmitting a ringing signal to saidsubscriber and for emitting a control impulse to said connector, and means for receiving said control impulses and thereby bringing* said ringing current emitting means into operation.

2. In an automatictelephone system, a plurality of subscribers lines and a toll exchange, a connector with means for transmitting a backward signal according as the wanted subscribers line is idle andrwith means for emitting ringing current to an idle subscribers line, means connected to said toll exchange` forV receiving said backward signal and-thereby switching in -an Y optical signal and emitting control impulses and means for receiving said control impulses and thereby bringing said ringing current emitting means into operation.

3. In an automatic telephone system according to claim 2, further means associated to said connector and responsive to said control impulses sent by said toll exchange for making said wanted subscribers line inaccessible to other toll calls.

4'. In an automatic telephone system, a calling exchange, a calling subscribers line connected to said calling exchange, a. called exchange, a wanted subscribers line connected to said called exchange, a trunk line connecting said exchanges, a connector associated to said called exchange and provided with means for transmitting a backward idle signal to the calling exchange when the wanted subscribers line is idle, a repeater connected to said calling subscribers line withinrsaid calling exchange and provided with means responsive to said backward idle signal for transmitting a forward control impulse, a counting device situated at said calling exchange between said repeater and said trunk line and provided with means for delaying the transmission of said forward control impulse to said trunk line, means arranged at said called exchange for emitting ringing current to said wanted subscribers line and means responsive to said forward control impulse for bringing into operation 9 said ringing current emitting means.

5. In an automatic telephone system a plurality of subscribers lines, a connector with means for transmitting a backward idle signal when the wanted subscribers line is idle and for transmitting a backward busy signal when said subscribers line is busy, ringing current emitting means associated to said connector, a repeater connected to a calling subscribers line and provided with means responsive to said backward busy signal for transmitting an audible busy tone to said calling` subscriber and for releasing the connector and with further means responsive to said backward idle signal for transmitting an audible ringing tone to said calling subscriber and a forward control impulse to said connector, and means associated to saidr connector and responsive to said forward control impulse for bringing into operation said ringing current emitting means.

6. In an automatic telephone system a calling exchange with at least a calling subscribers line, a called exchange with at least a wanted subscribers line, a trunk line connecting said exchanges having repeaters `at its ends, a connector situated `at said called exchange having means for transmitting a short backward idle signal when said wanted subscribers line is idle and a second short backward signal Vwhen the wanted subscriber replies and means for emitting ringing current to said wanted subscribers line, a repeater situated in said calling exchange and connected with said calling subscribers line having means responsive to said first short backward idle signal for transmitting an audible ringing tone to said calling subscriber and a forward control impulse to said connector and for preparing means for switching through the speech lines, said repeater having further means responsive to said second backward signal for making effective said prepared means for switching through the speech lines, means associated to said repeaters of said trunk line and responsive to said first backward idle signal for preparing means for switching through a conversation circuit, further means associated to said repeaters of said trunk line and responsive to said second backward signal for making effective said prepared switching through means and means associated to said connector and responsive to said forward control impulse for bringing into operation said ringing current emitting means.

7. In an automatic telephone system a trunk exchange, a called exchange, `at least a called subscriber connected to said called exchange, a trunk line connecting said exchanges, repeaters arranged at the ends of said trunk line, a connector arranged at said called exchange and provided with means for transmitting a short backward signal when the wanted subscriber is idle and a further short backward signal when said subscriber replies, with means for emitting ringing current to said wanted subscribers line with means for transmitting a permanent backward signal when said wanted subscriber is busy and with means for switching through to a busy subscribers line, means associated to said repeaters of said trunk line and responsive to two short backward signals for switching through a conversa-tion circuit, means associated to said trunk exchange and responsive to said permanent backward busy signal for transmitting a forward control impulse, means associated to said connector and responsive to said forward control signal for making ineffective said permanent backward signal transmitting means and for making effective said switching through means and means controlled by said switching through means for said connector for transmitting a short backward signal to said trunk exchange.

8. In an automatic telephone system a calling exchange, at least a calling subscriber, a called exchange, at least a called subscriber connected to said called exchange by a group of subscribers lines, a trunk line connecting said exchanges, repeaters arranged at the ends of saidtrunk line, a connector arranged at said called exchange and provided with means for testing a selected subscribers line actuable when said line is idle, with means for testing said group of subscribers lines actuable when a line of said group of lines is still idle, with means controlled by said group testing Ymeans for automatically stepping said connector onto an idle line of said group of subscribers lines, with means for transmitting a backward idle signal when said connector is stepped onto an idle subscribers line and with means, for emitting ringing current to said selected line, means associated to said calling exchange and responsive to said backward idle signal for transmitting an audible ringing tone to said calling subscriber and for transmitting a forward control impulse and means associated to said connector and responsive to said control impulse for bringing into operation said ringing current emitting means.

9. In an automatic telephone system according to claim 8, an impulse receiving relay associated to` said connector having a winding which is controlled by said group testing means.

l0. In an automatic telephone system a toll exchange, a called exchangaat least a wanted subscriber connected to said called exchange vby a group of subscribers lines, a trunk line connecting said exchanges, a connector associated to said called exchange having means for automatically stepping its switch arms onto the con-V l backward signals for switching through a conversation circuit and means associated to said connector for transmitting a second backward signal when said switch arms have reached a line of said group of subscribers lines being engaged only by an ordinary call.

12. In an automatic telephone system a calling exchange, a called exchange, at least a wanted subscriber connected to said called exchange, a

with repeaters at its ends, a connector arranged at said called exchange and provided with means for transmitting a short backward signal when the selected subscribers line is idle, for emitting ringing current to said subscriber and for transmitting a further short backward signal when the wanted subscriber replies, each of said repeaters comprising a transformer one winding of which being connected to said trunk line, an alternating current receiving relay connected to the other winding of said transformer, switching-through means for connecting the speech lines of the associated exchange to said receiving relay and said winding and means responsive to said two backward signals for controlling said switchingthrough means.

13. In an automatic telephone system a calling trunk line connecting said exchanges provided exchange, a called exchange, at least a Wanted subscriber connected to said called exchange, a connector arranged in said called exchange and provided with means for transmitting a direct current backward signal when said wanted subscriber is idle, with means for emitting ringing current to said wanted subscriber, and with means for transmitting a second direct current backward signal when said called subscriber replies, a trunk line connecting said exchanges and repeaters at the ends of said trunk lines provided with a transformer one winding of which being connected with said trunk line, with means for transmitting alternating current impulses over said trunk line, with an alternating current receiving relay operable also by direct current and connected with the other winding of said transformer, with means for connecting said winding and said receiving relay with the speech line of the associated exchange, with means responsible to said two direct current backward signals for controlling said alternating current transmitting means and said connecting mea-ns and with means controlled by said receiving relay when operated either by alternating current or by direct current for making ineffective said connecting means.

14. An automatic telephone system according to claim 13 in which said receiving relay comprises two windings being arranged in parallel and separated by condensers, one of said windings being directly switched across said speech line when said connecting means are eiective, the other of said windings being arranged in series with a condenser and with a winding of said transformer.

ALEXANDER WIRTH. ROLAND BECKER. 

